This invention relates generally to methods for modulating the metabolism and storage of lipids. The invention relates particularly to the use of lipid metabolism and storage modulators such as agonists or antagonists of hedgehog activity to alter the metabolism of lipids in the gastrointestinal tract, as well as to alter the storage of lipids in gut epithelial tissue.
Pathological conditions that affect storage, breakdown and intestinal absorption of lipids are included in a broad category of so-called xe2x80x9clipid metabolism disorders,xe2x80x9d and there are a variety of disorders that have been diagnosed. These include: diet-induced and regular hypercholesterolemia (Farese et al. Proc. Natl. Acad. Sci. USA 1995 92:1774-1778), abetalipoproteinemia and hypobetalipoproteinemia (Linton et al. J. Lipid Res.1993 34:521-541.) Several other lipid metabolism disorders of unknown origin have also been identified including Anderson""s disease (Anderson et al. Med. J. Aust. 1961 11:617-621), and atherosclerosis (Purcell-Huynh et al. J. Clin. Invest. 1995 95:2246-2257.) General symptoms of lipid metabolism disorders include, but are not limited to, chronic diarrhea, inadequate weight gain or weight loss, inability to lose excess weight and general failure to thrive. (Case 35-1999, New England Journal of Medicine; 327: 628-635 1992.) The various lipid metabolism disorders have been thought to originate through aberrant expression of apolipoproteins and/or regulation of genes responsible for various aspects of lipid metabolism.
Apo-B is synthesized by the intestine and the liver in mammals, where it serves as the main structural component in the formation of chylomicrons and the synthesis of very low-density (VLDL), low-density (LDL) and indetermediate (IDL) lipoproteins. The formation of chylomicrons by the intestine is very important for the absorption and transport dietary fats and fat-soluble vitamins. Genetically modified mice that express apo-B in the liver, but not in the intestine can not form chylomicrons. (Young et al. J. Cli. Invest. 1995 96:2932-2946.) In fact, apolipoprotein knockout mice exhibit early death (death at embryonic day 11.5) and impaired lipoprotein formation in the yolk sac. (Farese et al. Proc. Natl. Acad. Sci. USA 1995 92:1774-1778.)
The various lipid metabolism disorders are also thought to originate via malfunctions in embryonic tissue development. The generation of the intestines from the embryonic gut material depends solely on intercellular signaling between endodermal and mesodermal cells of the gut. It has been widely recognized that the hedgehog-signaling pathway plays a critical role in the direction of specialized mesoderm differentiation in the intestine and pancreas. (Apelqvist et al. Current Biology 1997 7:801-804.) Hedgehog is initially expressed in mouse embryos in the ventral part of the foregut endoderm, and has been shown to mediate endodermally derived signals in embryonic hindgut. (Id.) Specifically, mice with targeted deletion of hedgehog have evident foregut defects that are apparent as early as embryonic day 9.5, when the tracheal diverticulum begins to outgrow, suggesting that hedgehog and its signaling components are involved in foregut defects in humans. (Litingtung et al. Nature Genetics 1998 20:58-60.) See also Yang et al. Molecular Medicine 1997 3:826-835.
Many attempts to treat lipid metabolism disorders have been made with little practical success. (Case 35-1999, New England Journal of Medicine; 327: 628-635 1992.) There are currently no treatments that address lipid metabolism disorders by modulating their metabolism at the source, namely, the intestine. Nor are there any treatments that can potentially eliminate the disorder in and of itself. Therefore, it would be desirable to develop a method of treatment that could modulate lipid metabolism in the intestine. It would also be desirable to develop a method of therapy that could treat a lipid metabolism disorder for the sole purpose of substantially eliminating the disorder.
This invention is based on part on our discovery that the hedgehog-signaling pathway may play a role in the intestinal metabolism of lipids, including regulation of apolipoprotein expression, endogenous cholesterol synthesis and uptake of exogenous dietary cholesterol. Specifically, our discoveries support the role of the hedgehog-mediated signaling pathway in the metabolism and storage of lipids.
It would be useful to develop methods using hedgehog agonists or antagonists that would act as modulators of lipid metabolism and storage and, consequently, act as modulators of the effects and symptoms of certain lipid metabolism disorders. We have solved this problem by developing methods of modulating lipid metabolism and storage using hedgehog modulators that are capable of binding to the hedgehog receptor without eliciting signaling by hedgehog and, thus, serve as antagonists to hedgehog activity. We have also developed methods of modulating lipid metabolism and storage using hedgehog modulators that act as hedgehog antagonists by binding to the hedgehog protein and thus, inhibit or compete with hedgehog""s ability to bind to its receptor. Further, we have developed methods of modulating lipid metabolism and storage using modulators that are versions of hedgehog and related small molecules that are capable of binding to, or enhancing the binding affinity of hedgehog and, thus, act as agonists. Further, we have developed methods of modulating lipid metabolism using hedgehog modulators that are antibodies acting as as antagonists, in that they are capable of binding to hedgehog, and thus, block it from binding to its receptor.
One aspect of the present invention relates to a method for modulating lipid metabolism in a subject. Briefly, the subject method comprises administering a pharmaceutically effective amount of a composition containing a hedgehog modulator. The modulator can be either a hedgehog antagonist or agonist in a pharmaceutically effective amount.
In other embodiments, the methods of the present invention can be used to modulate the formation of vacuoles in gut epithelial cells in a subject.
In another embodiment, the methods of the present invention can be used to control the sequestering of lipids in gut epithelial cells.
In still other embodiments, the methods of the present invention can be used for preventing or for treating a variety of lipid metabolism disorders, including: preventing, treating or protecting a subject from cholesterol-related disorders; preventing or treating atherosclerosis; preventing or treating apolipoprotein disorders, including apo-B deficiency disorders; preventing or treating abetalipoproteinemia and normotriglyceridemic abetalipoproteinemia; for treating hypobetalipoproteinemia; for treating chylmicron-retention diseases; for treating vitamin A and E malabsorption and deficiency disorders; and for treating, preventing or protecting from obesity.
In one embodiment, the present invention provides a method for the treatment of a lipid metabolism disorder utilizing a pharmaceutically effective composition containing, as an active ingredient, a hedgehog modulator. In one of the preferred embodiments, the invention contemplates using a modulator to control lipid metabolism in a subject afflicted with a lipid metabolism disorder involving accumulation of lipid material in intestinal epithelial cells or tissues.
In another embodiment, the invention contemplates using a hedgehog modulator to modulate lipid metabolism in a subject afflicted with a lipid metabolism disorder, including, but not limited to, obesity.
In preferred embodiments, the hedgehog modulator is a hedgehog antagonist selected from the group consisting of a hedgehog mimetic, or an active fragment thereof; a modified hedgehog protein, or an active fragment thereof; a hedgehog variant; or an anti-hedgehog homolog. The anti-hedgehog homolog can be a human antibody, a chimeric antibody, a humanized antibody or any active fragments thereof.
In certain embodiments, the subject method is carried out using a modulator which is a hedgehog agonist that is capable of binding to the hedgehog receptor with, at least the same, if not a higher, binding affinity as the hedgehog protein.
Another aspect of the present invention relates to a therapeutic preparation of a small molecule hedgehog modulator therapeutic, in which the modulator is either a hedgehog antagonist or agonist provided in a pharmaceutically acceptable carrier in an amount sufficient to treat a lipid metabolism disorder.